Conventionally, the following technologies have been known as inter-atom force microscopes.
In such technologies, when scanning is conducted while causing a probe and a sample surface to approach one another, the very small inter-atomic forces operating between the atoms constituting the probe and the atoms constituting the surface of the sample are detected, and thereby, it is possible to observe with high resolution the extremely fine surface topography on a metal sample or an insulator sample.
The operating principle of the inter-atom force microscope is as follows.
In FIG. 6, reference numeral 601 indicates a probe having an overall size on the level of a few microns and having a pointed lead end; this probe comprises a material such as, for example, silicon nitride or the like. This probe 601 is formed integrally with a thin spring 602. Reference numeral 603 indicates a sample; such samples include metals, insulators, semiconductors, or the like. The forces operating between probe 601 and sample 603 vary as shown in the graph of FIG. 7 when the distance therebetween is altered. Here, the X-axis indicates the distance between probe 601 and sample 603, and taking the point at which this force is 0 as the origin, the direction in which the probe moves away from sample 603 is the positive direction. The Y-axis indicates the force operating between probe 601 and sample 603; the positive direction indicates a repulsive force, while the negative direction indicates an attractive force. An attractive force operates between the probe 601 and the sample 603 as they approach one another at a point at which the extreme surfaces thereof are at a distance of less than approximately 100.ANG., and a repulsive force operates therebetween when this distance is reduced to a few .ANG.. The size of the force is within a range of approximately 10.sup.-7 to 10.sup.-12 N. The repulsive force is converted to a displacement by means of a weak spring (10 N/m-0.01 N/m), and by means of this, the force operating between the probe 601 and the sample 603 can be determined.
There are cases in which an optical lever is employed as a method for detecting the displacement of the spring. A conceptual diagram showing the case in which an apparatus is constructed in this manner is shown in FIG. 8. The sample can be moved slightly and independently in each of the X, Y, and Z directions using piezoelectric elements 801 in the XYZ scanning system. The displacement detection system comprises a laser source 802 and a laser detector 803; these are disposed so that the laser beam reflected at the upper surface of the spring 805 which is formed integrally with the probe 804 is incidented into the laser detector 803. When a displacement is produced in spring 805 as a result of the force operating between probe 804 and sample 806, a change is produced in the path of the reflected laser in accordance with the displacement, and this displacement thus alters the amount of light which is incidented into laser detector 803, and the displacement is thus detected. In order to detect the changes in the extremely fine recesses and projections on the surface of sample 806 by means of probe 804 when scanning sample 806 in the X and Y directions, a method is often employed in which the displacement of the spring 805 is not directly measured, but rather, the sample 806 is moved in the Z direction in accordance with the recesses and projections thereon so that the displacement maintains a constant value, and the data relating to the recesses and projections is obtained from the piezo control voltage at that time.
The following methods are commonly employed as methods which permit the estimation of the amount of recesses and projections measured by means of this microscope.
1) Calibration is conducted by means of a grating pattern having recesses and projections on the level of from 1,000.ANG. to a few 100.ANG., from the limit in accordance with the manufacturing method of the stepped portion of the pattern and the measurement limit of another measurement apparatus when used on this stepped portion. PA0 2) The relationship between the voltage applied to the piezoelectric elements and the displacement is estimated in advance by means of an optical mechanism. PA0 3) A sample, the shape and degree of recesses and projections whereof is determined in advance by means of cross sectional TEM or the like is measured, and this is coordinated with the size of the recesses and projections, insofar as this produces no inconsistencies.
However, in the conventional technologies described above, the following problems were present.
The resolution of this instrument was far superior to that of other instruments, so that in the region in which the instrument was best capable of exhibiting its abilities, a region from a few tens of angstroms to a few angstroms or less, there was no other measurement mechanism capable of accurately calibrating the amount of recesses end projections.
In greater detail, with respect to 1), 2), and 3) described above,
1) when an attempt was made to estimate the recesses and projections on a level of 10.ANG. or less, at which level the inter-atom force microscope exhibited its abilities, the values calibrated by means of method 1) above were interpolated to values of 10.ANG. or less in an unchanged manner, and this is extremely dangerous, and is likely to produce conflicting values as a result of the characteristics of the instrument.
Method 2) above was effective for the calibration of the piezoelectric elements themselves; however, it is doubtful that these values will strictly correspond to the values obtained when the piezoelectric elements are built into an instrument as an inter-atom force microscope. Furthermore, such a calibration method requires a considerable level of technology, so that it is not a method which can be easily employed by a user at the site at which measurement is conducted.
The method of 3) is serviceable as a method for approximate calculation; however, the possibility of quantitive estimation using this method is poor.
The present invention has as an object thereof to provide a reference sample for the easy and accurate calibration of a region of recesses and projections within a range of a few tens of angstroms to a few angstroms, in which range an inter-atom force microscope displays superior performance.